Christina Holman | Design Blog

It's Wednesday, July 30th and that means I have less than 6 hours to fully prepare for my poster presentation tomorrow (and pack). This entire week I have fluctuated between PCB layout design in gEDA software and finalizing the internship, though I have made the personal decision to continue my involvement beyond this summer. This entire week has been very active and I barely have time to come up for air. Over the last few days, I have submitted several renditions of the PCB layout, resolving issues such as incorrect traces, lost files, placing components on a dual-sided PCB and more. Most Physics and EE students -- including my advisor -- do/did not design a PCB until graduate school. And, here I am, as a rising sophomore, creating my own PCB. As I mentioned before, this internship has given me more skills than I could possibly imagine. Updates: MUXs are placed on the back-side of the board and connected to the top components with "vias" Two distinct ground planes...

We're finally making headway on this project! We are very close to finishing the PCB (thanks to a few extra weekend work days) and could most likely finish the PCB layout tomorrow. After passing around several versions of pieces of the PCB board, using the gschem software, Dr. Phillips, Prof. Battat and I have redrawn electrical connections, replaced components with others, implemented PCB footprints in all the components, checked for back termination and proper voltage levels, and, overall, used the "divide and conquer" method. I started with a tutorial on gEDA schematic drawings, and, now, I am drawing complicated, detailed schematics on my own. Most first-year Engineering majors wouldn't have half as much exposure to such professional techniques as Dr. Phillips and Prof. Battat have allowed me. They're absolutely challenging me, but I wouldn't take back one minute of this experience. Over the last two days, I've received constant feedback from my ad...

People who know me have heard me constantly credit a high-school STEM program for my "Aha!' moment with electrical engineering and, yesterday, the program held its final presentations ceremony (and alum reunion) for its 39th year in a row. As a rising senior during MIT's Minority Introduction to Engineering and Science (MITES) ten-week summer program, I came in with my mind set on becoming a chemist but was placed in the Electronics design course (my second to last choice). I started the first day of class trying to calm my nerves: "Oh well. I'll make the best out of it." Before I knew it, I had run to call my parents, telling them "I know what I want to do with my life! I want to be an electrical engineer." And my course hasn't changed since. I really have to credit MIT Professor Joe Steinmeyer for developing my love for electronics and encouraging it (e.g. he photocopied his entire Getting Started in Electronics  by Forrest Mims for me)...

Thursday, Dr. Phillips, Prof. Battat and I met from 10am to 3pm to focus on the design for the printed circuit board (PCB) to be used with the final prototype. We didn't even look at the gEDA software but, rather, discussed the needed components and their layout on the board itself. Once we found a room with a sufficient amount of white boards, the team dived into drawings and note-taking. Over the past few days, in debugging the breadboard circuitry, we have discussed greatly about the impact of impedance and capacity with long wires. We tried to eliminate such unnecessary distances with grouping families together, i.e. all the MUXes in parallel rows. We also looked into the issue of single-point grounding between digital and analog electronics. On the breadboard, the addition of a MUX to the same voltage supply greatly affected the abilities of the counter and could distort the counting completely. Additionally, we discovered that the MUX and 4-bit counter had ...

With all the progress made last week with the counter, we still are having trouble seeing the correct Vout signal pattern of the MUX. Prof. Battat returned today and looked at the setup himself, and we made a few changes. Today was filled with lots of bumps and hills, and, at one point, we even thought we had burned out the counter and solder another just in case. In the book Moonwalking with Einstein , Foer states that humans sometimes reach a "plateau" where their progress or betterment at a task no longer increases. Nonetheless, he finishes by writing that one can overcome this stage by being extra-meticulous in their search for error. With 3 weeks left, it is time to be extra diligent in our work. The first change was to remove the 50 Ohm surface-mount, resistors on the MUX because it was affecting the counter's ability to count. Dr. Phillips and I were unsure how to address the issue earlier, but he suggested the use of buffers. The binary counter can drive 50 mA...

For the majority of this internship, I have neglected my second project with Larry in the machine shop, for which I has so much enthusiasm upon agreeing to do it. We have, however, been toying over how to go about creating this gyroscope between the original Youtube designs I found to a Solidworks homework design to a modified Solidworks file from a CAD community. We finally decided on the latter and modified the scale as well as the inner wheel, taking into account the stock we currently have in the shop and "reasonable" ranges for dimensions (see left). We quickly jumped into the project and, fortunately, I have experience on a few of the machines in the shop, which helped ease instructional time. Nonetheless, I did have to do a few exercises on a new machine: a (programmable) vertical mill with positioning edge, setting the center for the object I'm milling, etc. Larry wanted me to get comfortable with the machine first before using its programming features. In m...

With Battat gone for the rest of the week, Dr. Phillips came in Wednesday to help with the development of the project again. Since we debugged the counter in our last session, we wanted to focus on the debugging of the MUX eval board and see how it worked with the 16-channel signal simulator. Wednesday Session: Observations After soldering wires on to the A0 and A1 inputs as well as the V+, V- and Ground inputs of the board, we hooked it up and saw that the timing of the address lines were incorrect, although we had already checked to see the counter working perfectly. We also noticed that the Vout line of the MUX showed four levels of a voltage pattern -- one about .3V, a second and a third slightly above GND level, and possibly a fourth, which would indicate that the signal simulator is working properly with the MUX and ribbon cable. The voltage pattern from Vout followed proper operation however, since the signals on the MUX inputs were mixed using jumper wires to place high...

With Battat gone, Dr. Phillips came in this afternoon to help test the prototype of the address generator (the 74LVC161 binary counter and the 74LVC139A-Q1 2-to-4 line decoder). The least significant bits (LSBs) -- Q0 and Q1 -- of the counter are used as inputs to the four muxes for their individual channel-select features, while the most significant bit (MSBs) -- Q2 and Q3 -- will be used for the shutdown lines (SDs) to select which MUX chip is active. Why This Binary Counter? I don't believe I adequately explained our choice before, so I am doing so now. The binary counter is synchronous counter, meaning it feed all four flip-flops of the muxes in parallel, and the outputs Q0-Q3 define its present state from Count 0 to Count 15. Having a synchronous counter is much better than the alternative ripple counter, which causes each bit to lag behind its preceding one, i.e. Q1 lags behind Q0, at the expense of a 5-10 ns delay. We are building an analog MUX that connects 16 channel...

This morning, Battat and I met with Dr. Phillips about the project and I facilitated the meeting. We discussed: Hardware update: divider circuit, decoder/demux, etc. Delays in the glue logic and voltage diagram Potential causes for the irregular counting and debugging methods Muxes to ADC connection: Any barriers? Determining the gain for op-amps Next steps and plan for next week? We decided to test the MUX/ADC connection with termination only at the sending end -- the MUX amplifier -- otherwise called "back-end termination." Doing such will help in that reflections from the ADC will be adequately absorbed in the termination and will not reflect to make a confounding signal at the ADC input. We will determine whether it actually works by using the ADC to measure the overshoot when switching channels and then use the findings in the decision regarding termination for the next prototype. What's more, we found that the  ADS5292  demo board does not transmit direct...

With the project meeting agenda in the back of mind for tomorrow, I asked Battat to level with me about my progress, and, unfortunately, we are slightly behind on the project. To get this train back on track, I pulled into hyperspace, focusing on the hardware for the glue logic and compatibility between electronic components. 8-Pin Decoder mounted on PCB board  under a magnifying glass We were fortunate enough to receive our packages from Adafruit and the other pieces this week early on. I immediately dived into some largish-scale soldering with the mux eval boards. I made the ribbon cable for the divider circuit that I started wrapping up last week and then soldered the cable's ends to the eval board. Battat started placing some of the capacitors and resistors on the board today; I'm glad I did because that might have gotten messy without some guidance. small-scale soldering with these miniscule pieces, and Battat showed me some techniques in creating ...